​​​​Valuing multiple eelgrass ecosystem services: fish production and uptake of carbon and nitrogen

Billett D. - Deep Seas Environmental Solutions Ltd


In a recent open access paper Scott Cole (Enviro Economics Consultancy Sweden) and Per-Olav Moksnes (University of Gothenburg) have developed a framework for valuing multiple ecosystem services with relevance to the retention and restoration of eelgrass in the northern hemisphere (Frontiers in Marine Science 13 January 2016). They highlight the many complex trade-offs in the loss and/or restoration of eelgrass beds focussing on valuing nature's benefits to society in monetary terms. The work is of importance to policy-makers making decisions between competing demands in the coastal zone.

Seagrass beds are impacted by multiple stressors including nutrient pollution, sediment runoff, dredging, and coastal development (docks, marinas, etc.).  The global loss of seagrass ecosystems has led to a decline in key ecological functions such as habitat provision for fish and other organisms, uptake of carbon and nutrients, sediment stabilization and storm protection. As seagrass functions decline, so too do ecosystem services resulting in the reduction of economic goods that depend on them, such as food (e.g., fish and other seafood), the protection of real estate from coastal erosion, and clearer water and stable sandy beaches for recreation and tourism.

The authors quantified the value of eelgrass beds per unit area as habitat for fish, and the sequestration (uptake) of carbon and nitrogen.  They calculated that if a hectare of eelgrass is lost and the habitat transformed to unvegetated bottom where the top 5–25 cm of the sediment is eroded, a variety of losses would occur including: a reduced yield of approximately 626 kg of gadoid fish and 7535 individual wrasses, a reduction of 99,000 kg (98.6 tons) of sequestered carbon and 466 kg of nitrogen over a 20–50 year period. This produced a conservative value of economic benefits to be in the region of 20,700 US Dollars per hectare of eelgrass.


Figure 1. Eelgrass (Zostera marina). Photo credits to Kaire Kaljurand.


The work demonstrates the important benefits that arise from the retention and restoration of eelgrass beds with implications for commercial fishing, the mitigation of impacts from climate change and reducing eutrophication in coastal waters. Fish production, which is the most commonly valued ecosystem service in the seagrass literature, represented only 25% of the total value.  Benefits of nitrogen regulation constituted 46%, suggesting that most seagrass beds have been undervalued by previous studies.

Quantifying ecosystem services provides a strong theoretical basis for valuing nature's contribution to societal well-being. Coastal managers, for example, may use the method to decide whether to allow partial losses (from e.g., dredging) or to assess the value generated by off-setting compensation projects (e.g., eelgrass restoration). Valuation estimates can support arguments for establishing Marine Protection Areas.  The value associated with damaged resources is critical for implementing the Polluter Pays Principle (PPP), which underlies several EU Directives and suggests that operators, not the government, are responsible for internalizing the cost of environmental damage.